Measles (rubeoloa, First Disease) is a highly contagious viral infection causing a classic rash. It was once endemic in the United States, infecting 3-4 million people yearly and killing around five hundred.[1] The incidence of measles declined sharply after the introduction of the vaccine in the U.S. in 1963, and was declared "eliminated" (no longer endemic) in 2000. Cases still occurred but were imported and then spread briefly, being contained by a largely immune population. The elimination of measles in the U.S. has been put under threat since the mid- to late-1990s as vaccination rates dropped and cases rose.

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Measles is caused by the measles virus. It is classically described by the clinical triad of "cough, coryza (runny nose), and conjuntivitis (pink eye)." These, along with fever, are the first signs of the disease, making it initially indistinguishable from the common cold.

The classic red, bumpy rash appears on the body about 3-5 days after the cold symptoms, announcing itself as a case of measles rather than a cold. Unfortunately, the disease is contagious long before the rash appears.

Measles is one of the most contagious diseases known. It is often said that if a person with measles rides an elevator, a passenger can still catch it two hours later.

For most people, the cold symptoms and the rash resolve and all is well. Some people can go on to develop ear or lung infections or diarrhea, none of which is likely to be fatal. Still 0.1-0.2% will die from the lung or brain complications of measles (pneumonia or encephalitis, respectively).[2] The disease has two main neurologic complications:

Measles encephalitis is a swelling of the brain that occurs in about 0.1% measles victims and often leads to permanent brain damage.

More rare is subacute sclerosing panencephalitis (SSPE) is a horrifying, fatal neurologic disease that can appear up to a decade after measles infection.

Complications of measles are most common in children under 5-years old, adults over 20, pregnant women, and people with immunity problems.

In the pre-vaccination era, most children caught measles. Despite increases in hygiene and medical techniques, rates of measles stayed effectively the same. In fact, anyone born before 1957 is presumed to have had the disease and to be immune.

When the first vaccine was licensed, measles basically disappeared from areas with widespread vaccination programs (measles is still endemic in some countries in Europe, Asia, the Pacific, and Africa[3]).

Based on historical analysis of measles-infected vs. measles-vaccinated children, a 2015 analysis reported that it is likely that there is a long-term immuno-suppression caused by measles infection that increases the likelihood of fatality from other diseases.[4][5]

In highly contagious diseases such as measles, herd immunity (either from vaccination or prior exposure) needs to be 90-95% to prevent epidemics.[6] Unfortunately, the post-2001 numbers are rather worse, because of a loss of herd immunity following the rise of the anti-vaccination movement.